flake: drop flake-utils, refactor #6628

Job	Run time
Build the fuzzers	2m 26s
Run the fuzzers (fuzz_test, true)	2m 54s
Run the fuzzers (fuzz_date, false)	2m 49s
Run the fuzzers (fuzz_expr, true)	2m 53s
Run the fuzzers (fuzz_printf, false)	3m 10s
Run the fuzzers (fuzz_echo, true)	2m 52s
Run the fuzzers (fuzz_seq, false)	2m 8s
Run the fuzzers (fuzz_sort, false)	2m 23s
Run the fuzzers (fuzz_wc, false)	1m 53s
Run the fuzzers (fuzz_cut, false)	2m 24s
Run the fuzzers (fuzz_split, false)	1m 55s
Run the fuzzers (fuzz_tr, false)	1m 57s
Run the fuzzers (fuzz_env, false)	1m 53s
Run the fuzzers (fuzz_cksum, false)	1m 57s
Run the fuzzers (fuzz_parse_glob, true)	2m 55s
Run the fuzzers (fuzz_parse_size, true)	2m 18s
Run the fuzzers (fuzz_parse_time, true)	2m 49s
Run the fuzzers (fuzz_seq_parse_number, true)	3m 4s
	44m 40s

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